Interpretive Summary: Large-scale re-vegetation efforts to promote soil conservation and support farm income under the Conservation Reserve program (CRP) was beneficial to air and water quality by controlling soil erosion on highly erodible croplands across the U.S. To CRP landowners faced with expired contracts, alternate land use options include forage-livestock production or killing the grass cover and conversion back to row crop production. However, changes in soil organic matter and integrated management systems to conserve soil improvement accumulated during the CRP upon converting back to forage and crop production in semiarid regions are not well understood. After three years, management changes from CRP to intensive OWB forage and NT wheat production resulted in no overall change in soil total carbon content and may have led to small gain in organic matter at the very surface of the soil, compared to the OWBUF treatment, where OWB forage was harvested every year without the benefit of fertilizer applications. Using tillage to incorporate the OWB sod and prepare clean seedbeds for planting annual crops resulted in lower soil organic matter in the first 2" soil depth by ruling out the formation of a surface organic crust. In the short term, increasing the intensity of grass management or no-tillage production systems appeared to allow former CRP land managers to control erosion and maintain the organic matter status found under the CRP sod in regions of limited rainfall.

Technical Abstract:
Information was needed regarding changes in soil organic matter and management practices to conserve soil improvement accrued during the Conservation Reserve Program (CRP) upon returning these lands to agronomic production in semiarid regions. We determined the changes in soil carbon (C) in two CRP field soils after three years of intensive grass management and winter wheat production. The study sites were located on Dalhart fine sandy loam and La Casa-Aspermont clay loams found near Forgan and Duke, OK, respectively. Management changes from CRP to intensive Old World bluestem (OWB) forage and no-till (NT) wheat production resulted in no overall change in soil total C but led to the stratification and small gains of organic C in the 0-2" soil depth of the Dalhart soil, compared to the OWBUF treatment where OWB forage was removed every year without the benefit of fertilizer applications. In the La Casa-Aspermont soil, only the NT wheat system showed similar organic C gains in the surface 0-2" depth. Otherwise the remaining alternative land management systems did not cause any significant change in soil total and organic C. Using shallow tillage to destroy the OWB sod and prepare crop seedbeds appeared to lower organic C content in the first 2" soil depth of the Dalhart soil, possibly preventing the development of a surface organic matter crust. Therefore, increased intensity of forage management or no-tillage wheat production systems allow land managers of former CRP grasslands to maintain the organic matter status found under the CRP sod in regions of limited rainfall.